Barbara Illingworth Brown

Glycogen Storage Disease in Adults

Table 1 The glycogen storage diseases (GSD) include more than ten separate genetic defects that impair glycogen breakdown, primarily in liver or muscle or both. Even the types most frequently encountered (GSD-Ia and GSD-III) are uncommon, each with an incidence of approximately 1 in 100 000 births. Thus, no single institution has followed and reported on a large series of patients. The importance of several major complications was recognized only recently because only single cases were initially reported. Our study represents the largest number of adults with GSD-Ia and GSD-Ib to be included in one investigation and is the first to focus on clinical and social outcomes. Although two groups of investigators recently described the clinical course of patients with GSD in Europe and Israel, most of the patients studied were children [1, 2]. Relatively little information is available about adults with these diseases. We collected information on adults with GSD-Ia, GSD-Ib, and GSD-III in the United States and Canada in order to identify long-term complications that may be amenable to prevention and to determine the effect of the disease on education, employment, and family life. Table 1. SI Units Glycogen Storage Disease Types Ia, Ib, and III Glycogen storage disease type Ia results from deficient glucose-6-phosphatase activity in liver, kidney, and intestine [3]. Glucose-6-phosphatase is a single 35-kd protein [4]. When glucose-6-phosphatase activity is deficient, the liver is unable to hydrolyze glucose from glucose-6-phosphate that has been derived either from the metabolism of stored glycogen or from gluconeogenesis. Patients must depend on dietary carbohydrate to maintain euglycemia; during a fast of more than a few hours, the serum glucose concentration may decrease profoundly, and seizures are common in children. Mental retardation is uncommon, however, because the brain is protected by its ability to metabolize lactate that is present at high concentrations in the serum. Chronic hypoglycemia causes a sustained increase of counter-regulatory hormones, such as cortisol. In childhood, GSD-Ia typically results in poor growth and delayed puberty. Hyperuricemia occurs probably because ATP synthesis from ADP is driven by deamination of the AMP product to inosine that is subsequently metabolized to uric acid. Renal excretion of uric acid may also be decreased because lactate competes for the renal anion transporter. Fatty liver and hyperlipidemia result from the large influx of adipose-derived fatty acids into the liver in response to low insulin and high glucagon and cortisol concentrations. Anemia that is refractory to iron supplementation is believed to occur because of chronic disease. In untreated adults with GSD-Ia, the blood glucose decreases only to about 2.8 mmol/L (50 mg/dL) after an overnight fast. Symptomatic hypoglycemia is uncommon in untreated adults, but increases of counter-regulatory hormones probably persist. Adults with GSD-Ia have a high incidence of hepatic adenomas and focal segmental glomerulosclerosis [3, 5, 6]. The continuing abnormalities in counter-regulatory hormones, together with the hyperuricemia and hyperlipidemia, may be responsible for many of the complications observed in adult patients. Glycogen storage disease type Ib results from a deficiency of the glucose-6-phosphate translocase that transports glucose-6-phosphate into the lumen of the endoplasmic reticulum where it is hydrolyzed by glucose-6-phosphatase [3]. The translocase has not been purified. Without the translocase, glucose-6-phosphate cannot reach the hydrolytic enzyme; thus, patients with GSD-Ib are also unable to maintain euglycemia. The resulting metabolic consequences are identical in both forms of GSD-I. Because patients with GSD-Ib also have neutropenia and recurrent bacterial infections [3, 7], it seems likely that the glucose-6-phosphate translocase plays a role in normal neutrophil function. In GSD-III, glycogen debranching enzyme is deficient [3]. This enzyme is a 165-kd protein that contains two catalytic sites that are required for activity. The enzyme has been cloned and sequenced [8]. Normally, successive glucose residues are released from glycogen by glycogen phosphorylase until the glycogen chains are within four glucose residues of a branch point. The first catalytic activity of the debranching enzyme (oligo-1,4,-1,4-glucantransferase) transfers three of the remaining glucose residues to the terminus of another glucose chain. The second catalytic activity (amylo-1,6-glucosidase) then hydrolyzes the branch-point glucose residue. Three molecular subgroups of GSD-III have been well defined [9]; each is associated with enzyme deficiency in the liver and with childhood hypoglycemia. In adults with GSD-III, hypoglycemia is uncommon. As in GSD-I, poor growth may be prominent, but the growth rate increases before puberty, and adult height is normal [10]. Additionally, increases in transaminase levels provide evidence of hepatocellular damage, and liver biopsies show periportal fibrosis [10], perhaps related to the abnormal short-branched glycogen structure. In patients with subtype GSD-IIIb, enzyme activity and immunoreactive material are absent in liver but are present in muscle; these patients do not have a myopathy. Patients with GSD-IIIa (78% of cases) lack enzyme activity and lack immunoreactive material in liver and muscle. Patients with GSD-IIId (7% of cases) lack only the transferase activity but have normal immunoreactive material in liver and muscle. In patients with GSD-IIIa and IIId, muscle weakness may occur either in childhood or after the third decade. Cardiomyopathy is apparent only after age 30 years [9]. Treatment of Glycogen Storage Disease For only the past 10 to 15 years, children with GSD-Ia and GSD-Ib were treated with either intermittent uncooked cornstarch or a nocturnal glucose infusion given by intragastric tube. When euglycemia is maintained in this manner, growth and pubertal development are normal, and it is hoped that the late complications of GSD-I will be prevented. A high-protein diet was recommended for patients with GSD-III. Diet supplementation can increase the growth rate in children with GSD-III [11], but beneficial results on the myopathy have been less well documented. In this retrospective study of adults with GSD types Ia, Ib, and III, we found, in addition to complications frequently recognized, a high incidence of osteopenia and fractures and of nephrocalcinosis, kidney stones, and pyelonephritis. We describe the long-term outlook for adult patients with GSD who have not had optimal lifelong dietary glucose therapy. Methods Information on patients 18 years of age or older was obtained by contacting specialists in pediatric metabolism, endocrinology, gastroenterology, and genetics throughout the United States and Canada and by advertising through the Association for Glycogen Storage Diseases and The New England Journal of Medicine. No registries of patients with GSD are available. Information was included on living adult patients with GSD and patients who had died since 1967. Diagnosis of GSD had been confirmed by enzyme assay of each patient or of an affected sibling. Fifty-six physicians were individually contacted. Nineteen stated that they were not treating any adult patients with GSD. Thirteen physicians in private practice or at 1 of 12 medical centers filled out a detailed questionnaire or sent copies of clinic and hospital records that were reviewed by two of us. To obtain an estimate of how many patients might be missed by this survey, we reviewed records from a reference laboratory (Washington University) of 21 patients with GSD-Ia and of 21 patients with GSD-III who were diagnosed between 1955 and 1972. If still alive, these patients would now range in age from 18 to 64 years. Our study includes only 5 of these patients with GSD-I and 1 with GSD-III. Thus, this report incompletely represents North American patients with GSD who are currently older than 18 years of age. Clinical, radiographic, and laboratory findings at the latest visit were obtained, but data were not universally available for every item on the questionnaire. In analyzing each response, information was considered to be available only if specifically recorded; omission of information was not recorded as either a negative or a positive response. The presence of liver adenomas, nephrocalcinosis, or kidney stones was based on data from ultrasound or radiographic studies. The diagnosis of osteopenia was based on data from radiographic studies. The normal values for height were taken from the National Center for Health Statistics [12]. Normal values for serum chemistry tests [13] were used. Results Glycogen Storage Disease Type Ia Case Report Patient 1, a 43-year-old divorced father of one child, is a poultry farmer. A liver biopsy and enzymatic assay were obtained at 4 years of age because of poor growth, hypoglycemia without seizures, hepatomegaly, and frequent nosebleeds. Despite frequent meals, growth continued to be poor, puberty was delayed, and the final adult height of 168 cm was achieved after 20 years of age. Allopurinol was taken inconsistently after one of many gouty attacks beginning from 18 years of age. The patient did not complete high school. As an adult, he has smoked 2 to 4 packs of cigarettes per day. After divorcing in his 20s, he frequently skipped breakfast and failed to follow a recommended diet. Instead, his diet was high in fat and consisted primarily of foods that required little preparation, such as candy and sandwiches. He has always denied symptomatic hypoglycemia, although his serum glucose concentration after an overnight fast is about 2.8 mmol/L (50 mg/dL). Beginning in his mid-20s, he had recurrent episodes of flank pain and hematuria that were treated with antibiotics, and he passed kidney stones. At age 24, an intravenous pyelogram showed punctate calcificati

Hepatic fructose-1,6-diphosphatase deficiency: A cause of lactic acidosis and hypoglycemia in infancy

An 8-month-old female, maintained on breast feeding for 6 months, experienced numerous attacks of hyperventilation when weaned to baby food and was admitted with severe lactic acidosis (20 mM) and hypoglycemia. Physical examination was negative except for hepatomegaly. Fasting (18 hr) after stabilization on a high carbohydrate diet resulted in hypoglycemia (plasma glucose 40 mg/100 ml), lactic acidosis (6-10 mM), and a rise in plasma alanine. Glucagon produced a glycemic response after 6 hr, but not after 18 hr fasting. Intravenous galactose increased plasma glucose (Delta 45 mg/100 ml) but intravenous fructose, glycerol, and alanine caused a 40-50% fall in plasma glucose and a significant rise in lactate (Delta 3-4 mM). Liver biopsy showed fatty infiltration. Liver slices incubated with galactose, lactate, fructose, alanine, or glycerol converted only galactose to glucose. Hepatic glycolytic intermediates were increased below the level of fructose-1,6-diphosphate and decreased above. Hepatic phosphorylase, glucose-6-phosphatase, amylo-1,6-glucosidase, phosphofructokinase, fructose-1-phosphate aldolase, and fructose-1,6-diphosphate aldolase levels were normal, but no fructose-1,6-diphosphatase (FDPase) activity was detected. Further studies on the liver homogenate of this patient revealed the presence of an acid-precipitable activator of FDPase. Normal plasma glucose and lactate levels were maintained on an 800 cal diet of 66% carbohydrate (sucrose and fructose excluded). 5% protein, and 20% fat. When carbohydrate was reduced to 35% and protein or fat increased to 23 and 53% respectively, lactic acidosis and hypoglycemia recurred. These studies show that a deficiency of FDPase produced infantile lactic acidosis and hypoglycemia and can be controlled by an appropriate diet.

Liver transplantation for type IV glycogen storage disease

Type IV glycogen storage disease is a rare autosomal recessive disorder (also called Andersen’s disease1 or amylopectinosis) in which the activity of branching enzyme alpha-1, 4-glucan: alpha-1, 4-glucan 6-glucosyltransferase is deficient in the liver as well as in cultured skin fibroblasts and other tissues.2,3 This branching enzyme is responsible for creating branch points in the normal glycogen molecule. In the relative or absolute absence of this enzyme, an insoluble and irritating form of glycogen, an amylopectin-like polysaccharide that resembles plant starch, accumulates in the cells. The amylopectin-like form is less soluble than normal glycogen, with longer outer and inner chains and fewer branch points. The clinical onset of the disease is insidious, with nonspecific gastrointestinal symptoms at first, followed by progressive hepatosplenomegaly, portal hypertension, ascites, and hepatic failure. Children with this disorder usually die of hepatic cirrhosis by the age of two to four years. 4–8 In exceptional cases, cardiomyopathy,5–7,9 neurologic syndromes — including tremors, seizures, and dementia10,11 — or variable manifestations of myopathy5,12,13 have been reported. In patients with these unusual symptoms, the clinical onset is frequently later than in typical cases, and death most often results from cardiac failure. Liver transplantation for Type IV glycogen storage disease was attempted in 1972; the recipient died 110 days later after the rejection of the first liver transplant and attempted re transplantation.14 Liver transplantation was first performed successfully in September 1984 in Patient 1 of this series; since that time we have treated six more such patients. Our experience with these seven patients forms the basis of this report.

[88] Enzymes of glycogen debranching: Amylo-1,6-glucosidase (I) and oligo-1,4→1,4-glucantransferase (II)

Publisher Summary This chapter describes the specific oligosaccharide substrates for the separate measurement of each enzymatic activity (I and II). The nature of the reaction catalyzed by II is demonstrated using these substrates. Enzymes I and II act with phosphorylase to bring about the total degradation of glycogen to glucose 1-phosphate and glucose. The amylo-l,6-glucosidase appears to act directly on a polysaccharide limit dextrin to form glucose from its outermost branch points. The separate activity of amylo-l,6-glucosidase (I) is measured with certainty only when the substrate used is a branched oligosaccharide with the general structural features of B 5 . A limit dextrin (LD) of glycogen may not be a specific substrate for (I), as the number of exposed branch point glucose residues in the LD is not known with certainty. The initial rate of glucose formation from an LD may depend only on the action of (I) and be independent of the prior action of (II). The enzymatic activity of Oligo-l,4 → 1,4-glucantransferase (II) consists of the transfer of terminal maltosyl and, to a greater extent, maltotriosyl residues from α-l,4-1inkage in one chain to α-l,4-1inkage in another. The reagents used, procedure followed, and the steps involved in the purification are also described in the chapter.

Metabolic and biochemical studies in fructose 1,6-diphosphatase deficiency.

A 9-month-old girl with recurrent episodes of hypoglycemia, metabolic acidosis, and hepatomegaly was identified as having fructose 1, 6-diphosphatase deficiency on the basis of absence of activity of this enzyme in liver and in white blood cells. Fructose 1, 6-diphosphatase present in white blood cells of normal persons appears to be similar to the enzyme in liver and kidney with regard to pH optima, electrophoretic mobility, and inhibition by adenosine monophosphate. In contrast, fructose 1, 6-diphosphatase from muscle appears to be a distinct enzyme. The early diagnosis of this deficiency disorder is important as dietary restriction of fructose, sucrose, and sorbitol appears to be of value in the management of this potentially fatal inborn error of gluconeogenesis.

The subcellular distribution of enzymes in type II glycogenosis and the occurrence of an oligo-α-1,4-glucan glucohydrolase in human tissues

Summary Biochemical analyses of the tissues from a case (B.J.P.) of Type II glycogenosis revealed generalized storage of glycogen of normal structure, the lack of an α-glucosidase active at pH 4.5, and the presence of all other enzymes whose deficiencies have been implicated in other types of glycogenosis. Differential centrifugation of a sucrose homogenate of an unfrozen sample of liver taken by biopsy from this case showed that more than 50% of the activities of glucose-6-phosphatase (EC 3.1.3.9), uridine diphosphoglucose—α-glucan transghico-sylase (EC 2.4.1.11), α-amylase (EC 3.2.1.1), and of an α-glucosidase active at neutral pH were recovered in the 100 000 × g pellet which also contained most of the glycogen of the tissue. Investigation of the substrate specificity of the α-glucosidase at pH 7.1 showed that it was a hitherto unrecognized type of oligo-α-1,4-glucan glucohydrolase. This enzyme formed no glucose from glycogen but acted rapidly on oligosaccharides (maltose and maltotriaose) to yield glucose. The enzyme has been found in biopsy and autopsy liver samples from ten individuals and in nineteen skeletal muscle samples representative of a vaiiety of types of glycogen storage disease.

[67] α-1,4-glucan: α-1,4-glucan 6-glycosyltransferase from mammalian muscle

Publisher Summary This chapter discusses the synthesis of α-1,4-glucan 6-glycosyltransferase from mammalian muscle. The assay depends on the increase in the rate of formation of polysaccharide from G-1-P by phosphorylase on addition of the branching enzyme. In the absence of branching enzyme, long amylase chains are formed by de novo synthesis. This reaction is extremely slow, as the concentration of end groups with which phosphorylase reacts remains very low. In the combined enzyme system the increased number of end groups that arise as a result of the branching of the growing polysaccharide chain allows the phosphorylase reaction to proceed at a faster rate. In this system, the formation of orthophosphate is an indirect measure of branching enzyme action. In an alternate assay procedure, the decrease in optical density of the iodine complex of corn amylopectin is described by Larner as an assay for the action of the branching enzyme from rat liver. The branching enzyme acts slowly on long linear chains of α-l,4-1inked glucose units. It is found that while liver glycogen does not serve as a substrate for branching, amylose and the limit dextrin of amylopectin prepared by β-amylase can serve as substrates.

Liver transplantation for type I and type IV glycogen storage disease

Progressive liver failure or hepatic complications of the primary disease led to orthotopic liver transplantation in eight children with glycogen storage disease over a 9-year period. One patient had glycogen storage disease (GSD) type I (von Gierke disease) and seven patients had type IV GSD (Andersen disease). As previously reported [19], a 16.5-year-old-girl with GSD type I was successfully treated in 1982 by orthotopic liver transplantation under cyclosporine and steroid immunosuppression. The metabolic consequences of the disease have been eliminated, the renal function and size have remained normal, and the patient has lived a normal young adult life. A late portal venous thrombosis was treated successfully with a distal splenorenal shunt. Orthotopic liver transplantation was performed in seven children with type N GSD who had progressive hepatic failure. Two patients died early from technical complications. The other five have no evidence of recurrent hepatic amylopectinosis after 1.1–5.8 postoperative years. They have had good physical and intellectual maturation. Amylopectin was found in many extrahepatic tissues prior to surgery, but cardiopathy and skeletal myopathy have not developed after transplantation. Post-operative heart biopsies from patients showed either minimal amylopectin deposits as long as 4.5 years following transplantation or a dramatic reduction in sequential biopsies from one patient who initially had dense myocardial deposits. Serious hepatic derangement is seen most commonly in types I and IV GSD. Liver transplantation cures the hepatic manifestations of both types. The extrahepatic deposition of abnormal glycogen appears not to be problematic in type I disease, and while potentially more threatening in type IV disease, may actually exhibit signs of regression after hepatic allografting.

The molecular heterogeneity of purified human liver lysosomal α-Glucosidase (acid α-Glucosidase)

Abstract An α-glucosidase active at acid pH and presumably lysosomal in origin has been purified from human liver removed at autopsy. The enzyme has both α-1,4-glucosidase and α-1,6-glucosidase activities. The K m of maltose for the enzyme is 8.9 m m at the optimal pH of 4.0. The K m of glycogen at the optimal pH of 4.5 is 2.5% (9.62 m m outerchain end groups). Isomaltose has a K m of 33 m m when α-1,6-glucosidase activity is tested at pH 4.2. The enzyme exists in several active charge isomer forms which have p I values between 4.4 and 4.7. These forms do not differ in their specific activities. Electrophoresis in polyacrylamide gels under denaturing conditions indicates that the protein is composed of two subunits whose approximate molecular weights are 88,000 and 76,000. An estimated molecular weight of 110,000 was obtained by nondenaturing polyacrylamide gel electrophoresis. When the protein was chromatographed on Bio-Gel P-200 it was separated into two partially resolved active peaks which did not differ in their charge isomer constitution or in subunit molecular weights. One peak gave a strongly positive reaction for carbohydrate by the periodic acid-Schiff method and the other did not. Both had the same specific activity. The enzyme was antigenic in rabbits, and the antibodies so obtained could totally inhibit the hydrolytic action of the enzyme on glycogen but were markedly less effective in inhibiting activity toward isomaltose and especially toward maltose. Using these antibodies it was found that liver and skeletal muscle samples from patients with the “infantile” form or with the “adult” form of Type II glycogen storage disease, all of whom lack the lysosomal α-glucosidase, do not have altered, enzymatically inactive proteins which are immunologically cross-reactive with antibodies for the α-glucosidase of normal human liver.

CHAPTER 5 – Glycogen-Storage Diseases*: Types I, III, IV, V, VII and Unclassified Glycogenoses

Publisher Summary This chapter discusses glycogen-storage diseases and some of the rarer types in which still other enzymic deficiencies have been implicated. Hepatic glucose 6-phosphatase is a microsomal enzyme with an optimum for activity between pH 6 and 7. Children lacking glucose 6-phosphatase are subject to hypoglycemia but frequently are asymptomatic at extremely low blood-sugar levels. In Type III glycogenosis, a polysaccharide accumulates whose structure resembles that of the limit dextrin produced by the degradation of glycogen by phosphorylase. As in Type I glycogenosis, the infant with limit dextrinosis has hepatomegaly, may be hypoglycemic, and when in the fasting state, fails to show a glucemic response to epinephrine or glucagon. The four most commonly encountered types of glycogen-storage disease are Types I, II, III, and VI, where VI is characterized by polysaccharide storage in the liver (and no evidence for muscle involvement) with no known enzymic cause.